Change in the meaning of diagnostic concepts in psychiatry.

Transitions in the categorization of variables can contribute to changes in the concept of a psychiatric disorder. These transitions can occur with expansion of knowledge and without a concomitant change in the form of diagnostic labels. For example, the definitions of "mass" within the framework of Newtonian and Einsteinian theory are incompatible even though the same label is used to denote both concepts. Implications of the principles discussed for theory and practice in psychiatry are emphasized.